Recently, in the field of paint, in order to save natural resources and deal with pollution, aqueous paint containing an extremely small amount of organic solvent or aqueous paint without containing organic solvent has been frequently used.
In addition, owing to remarkable progress of technology for aqueous paint, the high-grade finished appearance which has been attained only by solvent-type paint has become to be realized even by the use of an aqueous paint.
However, in metallic paint containing a metal pigment such as aluminum or zinc, the practicable aqueous paints are hardly known. This is because a metal pigment easily corrodes in an aqueous paint. When metal powder is present in aqueous paint, corrosion due to water occurs in any one of acidic, neutral or basic region or two or more thereof, depending upon the nature of the metal used as the metal powder. As a result, hydrogen gas occurs. The occurrence of hydrogen gas is an extremely significant problem in view of safety when paint makers use paints and when automobile makers, home electronics makers, and industrial coating makers use paints.
The corrosion resistance of a metal pigment in water or aqueous paint is hereinafter referred to as “storage stability” so that it can be distinguished from aging stability of a metal pigment itself is.
JP-A-2000-7939 discloses metal particles containing a molybdate pigment. JP-A-6-57171 discloses a method of coating the surfaces of aluminum flakes with a molybdic acid film. However, even in the prior art disclosed in these earlier applications, the problems that the aging stability of an aluminum pigment itself and the color-tone of an aluminum pigment decrease are inevitable.